1. Field of the Invention
The present invention relates to an information processing apparatus and an information processing method.
2. Description of the Related Art
Conventionally, in the information processing field, information of multi-dimensional arrays has frequently been processed. Among them, in a part of processing and statistical processing pertaining to image processing, image recognition and image synthesis, the total sum value of elements in a range of a specific area is often acquired and used.
In recent years, in the field of computer graphics, a concept of cumulative image information with respect to original input image information has been proposed; this concept is referred to as the rectangular, summed-area table (e.g., see F. C. Crow, “Summed-Area Tables for Texture Mapping”, Computer Graphics, 1984).
According to the above document, the total sum value of elements in a rectangular area in an input image is calculated according to Equation (1). Here, it is provided that the summed-area table is a two-dimensional array with a size (the identical number of elements) identical to that the input image and the pixel value at the coordinate position (x, y) in the input image is I(x, y), C(x, y) is acquired as the total sum value thereof.
                              C          ⁡                      (                          x              ,              y                        )                          =                              ∑                                                            x                  ′                                ≤                x                                                              y                  ′                                ≤                y                                              ⁢                      I            ⁡                          (                                                x                  ′                                ,                                  y                  ′                                            )                                                          (        1        )            
For example, as illustrated in FIG. 2, a value C(x, y) of the summed-area table 20 at a position (x, y) is the total sum value of elements in a rectangle whose diagonal vertices are the origin position (0, 0) and the position (x, y) in an original input image 10. In the above document, description is made such that the origin position of the summed-area table is located at the lower left corner of the image.
This method can acquire the sum of pixel values I(x, y) in any rectangular area disposed horizontally or vertically on the input image only by referring to four positions in the summed-area table. For example, as illustrated in FIG. 3, the total sum C(x0, y0; x1, y1) of pixel values in the rectangular area whose diagonal vertices are (x0, y0) and (x1, y1) can be acquired by calculating Equation (2).C(x0,y0;x1,y1)=C(x0−1,y0−1)−C(x0−1,y1)−C(x1,y0−1)+C(x1,y1)  (2)
Therefore, this method can acquire the total sum of pixel values in any rectangular area in the input image at high speed.
In the field of image recognition, the integral image has been proposed as cumulative image information equivalent to the summed-area table (e.g., see P. Viola, M. Jones, “Rapid Object Detection using a Boosted Cascade of Simple Features”, Proc. IEEE Conf. on Computer Vision and Pattern Recognition, Vol. 1, pp. 511-518, December 2001). A fast face detecting process has been realized by an image processing apparatus. This apparatus includes a configuration that cascade-connects weak classifiers including a plurality of rectangular filters employing the integral image.
However, in order to acquire the total sum of the elements in the rectangular area in the processing window using the cumulative image information, cumulative image information corresponding to the entire pixel positions in the input image information should be prepared. This offers a problem of consuming a lot of memory resources for holding the cumulative image information.
The present invention is made in view of such a problem. It is an object of the present invention to reduce memory resources necessary to hold the cumulative image information.